Irradiation effects of a 10 MeV neutron beam on a Nd–Fe–B permanent magnet

The effects of irradiation of a Nd–Fe–B permanent magnet by fast neutrons was investigated. The decrease in measured magnetic flux density at the center of the magnets were 0.6%, 6.9%, 25.2% and 47.3% after continuous irradiation of 1.1 kGy, 3.7 kGy, 5.6 kGy and 7.4 kGy, respectively. On the other hand, the decrease due to non-continuous irradiation, in which the magnet was first irradiated at 3.7 kGy, then irradiated again at 3.7 kGy nine months later, was 14% smaller than that of continuous irradiation, even for the same total dose. The temperature coefficient of the magnetization did not change with irradiation. Some radioactive materials, such as 147Nd, 151Pm, and 54Mn, were detected in the magnet after irradiation.